Answer
$cos(2\theta)=2cos^2\theta-1$
Work Step by Step
If we know $cos\theta$, it is best to use the formula $cos(2\theta)=2cos^2\theta-1$
Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)
by Sullivan III, Michael
Published by
Pearson
ISBN 10:
0-32193-104-1
ISBN 13:
978-0-32193-104-7
Chapter 6 - Analytic Trigonometry - Chapter Review - Review Exercises - Page 528: 87
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